Six Sigma
By Wayne Tollefson
January 2004 marks the beginning of a new column in the Chicago Section Newsletter. The focus of this column will be a presentation of a case study in which a company learned and applied the methodology and techniques of Six Sigma to one of its key manufacturing processes. The case study will clearly demonstrate the power of, and the broad-based benefits to be derived from, the use of statistical thinking and methods for quality and productivity design and improvement. Throughout the case study, the Process Improvement (PI) Team will have an opportunity to use many tools from the Six Sigma toolbox as they seek to reduce defects, increase customer satisfaction and show a positive return on investment. The story is real, and the results are dramatic.
The Dilemma
A certain manufacturer of gaskets for automotive and off-road vehicle applications awoke one morning to find that a major customer had significantly tightened the bilateral specification on the overall thickness (TD) of a hard gasket used in automotive engines. Although the process demonstrated acceptable capability to the current specification, process capability to the new specification was unacceptable. Figure 1 below illustrates the difference in process capability between old and new specifications. The data used to calculate both process capability indices below remained the same; only the specification limits changed by a factor of 2.
Figure 1
The first reaction of the gasket manufacturer was to negotiate with the customer to obtain relaxation of the new specification. When efforts in this regard failed, the relationship between customer and supplier became somewhat strained. At first, the gasket manufacturer thought that if he waited long enough, the automotive company would eventually be forced to loosen the requirements and purchase the existing product. However, as time went on it became clear that some positive steps would have to be taken in order to restore the process capability to its previous level, that being Cpk = 1.51. But what should be done? And by whom? As George Box is fond of saying ‘What do we do now?’
Next month we observe how this troubled company begins its journey toward achieving Six Sigma quality. Looking forward to seeing you then.